Heretofore, studies have been made on the application of heat-resistant polymers such as polyimide, polyamide or polyhydantoin as the organic passivation film, surface protecting film, interlayer insulating film, etc., of semiconductor elements, on account of their superior heat resistance, electrical insulation, and mechanical strength. Unfortunately, these heat-resistant polymer films have poor adhesion to the surface of an element such as silicon wafer or glass. Those films do not stabilize the surface of element and rather decrease the reliability of semiconductor elements.
Several methods have been proposed to improve the adhesion of the above heat-resistant polymer films. One of them is concerned with a polyimide. According to this method, a polyimide precursor for polyimide is produced by polymerizing an aromatic tetracarboxylic dianhydride and diaminosiloxane in place of a diamino compound. The polyimide produced according to this method has in its molecular skeleton the Si-O-Si linkage derived from the diaminosiloxane. Owing to this linkage which bonds to silicon atoms in silicon wafer or glass, the resulting polyimide film is improved in adhesion to a silicon-containing material.
The polyimide film produced according to the above method is improved in adhesion but is poor in moisture resistance when used as a passivation film, because the diaminosiloxane accounts for most or all of the diamino compound. Moreover, the excessive diaminosiloxane is not preferable for the inherent properties of polyimide such as heat resistance, electrical insulating properties, and mechanical strength.
There is also proposed a method for producing a polyimide from a mixture of polyimide precursors, one being synthesized with an excess amount of diaminosiloxane and the other being synthesized with a diamine containing no silicon atom in its molecule. The polyimide produced according to this method has the same disadvantage as mentioned above because the mixture contains a large amount of silicon. Moreover, the polyimide produced from a mixture varies its adhesion, moisture resistance, and other properties between the lots.